The present invention relates generally to smoke and fog generators and especially to a low cost, fast startup resistance tube smoke generator.
A variety of training devices are available for generating nontoxic smoke for educational, theater, aerosol dispensing purposes. One such device of the prior art simulates smoke by utilizing steam mixed with an organic liquid so as to produce a vaporized organic liquid, and forcing the vaporized organic liquid through a narrow orifice into the atmosphere so that the vapor is rapidly chilled. While performing satisfactorily for its intended purpose of generating smoke, this prior art device ordinarily leaves something to be desired, especially from the standpoints of design complexity, cost effectiveness, energy utilization efficiency, and physical size.
In addition, there are commercially available a variety of smoke bombs or smoke grenades for generating smoke. These devices work well for their intended purpose of producing smoke, but leave something to be desired from the standpoints of cost effectiveness and personal safety, in that the smoke produced thereby may be toxic.
U.S. Pat. No. 2,882,240 to Charwat discloses a smoke generator primarily for use in a wind tunnel, that heats oil to a temperature below its boiling point and plays cool air over the oil to condense the vapor. The resulting smoke is removed through tubes of relatively large diameter.
U.S. Pat. No. 3,234,357 to Seuthe discloses an electrically heated smoke producing device in which a tubular element having a capillary bore through which an electrical heating element extends that is suspended in a liquid which will vaporize to form smoke when heated.
U.S. Pat. No. 3,250,723 to Fortney discloses a portable smoke generator that has a converter element which is heated, and sprayed with a smoke-producing fuel. A stream of air is directed by the converter to cause movement of the smoke from the converter.
U.S. Pat. No. 4,326,119 to the present inventor is the most relevant art. It discloses a portable battery-powered electric smoke generator for simulating the smoke of a fire for training purposes, that includes a tubular housing enclosing a rechargeable battery power supply having terminals connected to the ends of a tubular metallic coil filled with a vaporizable smoke producing liquid. One end of the tubular coil communicates with a smoke discharge port at one end of the housing. The discharge port is sealed by a fusible disk and communicates with an apertured smoke release cup. An electric switch arrangement, either thermal or electronic, is provided on the housing in the circuit between the coil and power supply for energizing the tubular coil for a time sufficient to superheat the vaporizable liquid therein. The heat of the tubular coil melts the fusible disk to release the superheated liquid through the smoke release cap into the atmosphere as a vapor simulating smoke. The liquid may be mineral oil, polyethylene glycol or propylene glycol.
U.S. Pat. No. 4,349,723 to the present inventor discloses a non-toxic smoke generator for simulating the smoke of a fire, that includes an inner cylindrical shell surrounded in spaced relation by a thermally insulated outer casing to form an air flow passage therebetween through which compressed air heated by electric air heaters is caused to flow in a helical pattern to heat the shell to a temperature above the vaporization temperature of a vaporizably smoke substance. The smoke substance, such as propylene glycol, polyethylene glycol 200 or mineral oil, is pumped from a reservoir through a supply pipe having a coiled preheating portion disposed in the space between the shell and housing and is sprayed through a wide spray atomizing nozzle into heated vaporization chamber where it is vaporized and discharged as non-toxic smoke.
U.S. Pat. No. 4,477,395 to Albarda discloses apparatus for admixing liquid anesthetics and respiratory gas to be supplied to a patient. The apparatus comprises a mixing chamber having an inlet for receiving the liquid anesthesia and the respiratory gas, and an outlet for supplying the mixture. A feed line is provided in the inlet for the liquid anesthesia, with a heat exchanger for equalizing the inlet temperatures of the anesthesia and respiratory gas. Temperature sensors are provided in the inlet and the outlets with a circuit for determining the difference between the temperatures. Without heating of the chamber, this difference is proportional to a ratio between the evaporated anesthetic and respiratory gas. With the chamber heated to equate the inlet and outlet temperatures, the amount of heating is proportional to the flow of anesthetic to the chamber.
In addition to these prior patents, the Applicant has also disclosed a beryllium oxide ceramic disc utilized to isolate the electrical circuit associated with the heating function of a long coiled thin wall tube smoke generator system from the other components of the smoke generator.
Other U.S. patents of interest may be seen in the U.S. Pat. Nos. 3,242,098, to Andrews; Kenney 3,255,967; Kerivily 3,355,571; Curtis et al 3,458,948; Slater et al 3,496,668; and Stevens et al 4,343,719. These patents show various smoke generators, foggers, and aerosol producers which are electrically operated and with heating coils. In addition to these, there are smoke generators, foggers, and aerosol producers which operate on propane or other liquid or gaseous fuels and which operate from the exhaust of automobile or lawnmower engines.
The present invention is an improvement on my prior U.S. patents and inventions and provides for a smoke, fog, or aerosol producer having a coiled electrical resistance heating tube mounted in an electrical circuit for applying an electrical voltage thereacross to heat the coil for heating a liquid being fed thereinto to produce smoke particulates by condensation of the superheated vapors in the ambient air. The tubing in this case is coated with a thin coating which allows the coil loops to almost abut against each other because of the electrical insulation of the coating while producing a high thermoconducting material of conducting heat rapidly through the coils to speed up the flow of heat from the hot end to the cold end of the coiled electrical resistance heating tube. This allows inexpensive thermostats to be used to measure the temperature at positions on the tube to operate a pump to feed a smoke agent material thereto when the tube reaches a predetermined temperature and to maintain heater temperature. The aim of the invention is to permit the use of a low cost thermostat in place of expensive solid state temperature controls while retaining the fast startup feature of a resistance tube smoke generator.